The invention relates to electronic assembly packaging in general, and, more particularly, the invention relates to a method and apparatus for shielding electrical components mounted on a printed circuit board from electromagnetic and radio frequency interference.
The current trend in the electronics industry is to miniaturize components and circuits and to place as many of the components and circuits next to each other as possible to provide quality technical performance in a small package. Any device that conveys electrical signals, such as a wire, a printed circuit board (PCB), an integrated circuit (IC) and the like radiates and is (typically) susceptible to electromagnetic interference (EMI) and/or radio frequency interference (RFI). Electromagnetic interference and radio frequency interference effect devices by corrupting or altering the electrical signal that the device conveys. Such corruption of an electrical signal in a device is usually not tolerable. Thus, it is critical that these devices be shielded from each other and other electromagnetic and radio frequency interferences.
In devices such as digital satellite receivers, EMI and RFI shields are made of tinplate sheet metal and are wave soldered directly onto the PCB. It is critical that a continuous solder joint is made between the shield and the ground plane of the PCB, which acts as a shield on the bottom of the circuit board. Because of their relatively large size, the shields have a high thermal capacitance. When the combination of the shield and PCB are processed through a wave solder machine, a large amount of the heat is conducted into the shield and away from the solder joint being formed. As a result, the area to be soldered may not reach optimal temperature for proper soldering. This results in cold solder joints or solder voids wherein gaps are created in the shield""s performance.
One prior art method to overcome the problem is to use pre-heaters inside the wave solder machine to heat the PCB combination before the PCB combination passes through the wave solder machine. However, the correct balance of heat is difficult to control and maintain using this technique.
A second prior art method to overcome the problem is to use multi-layer PCBs having plated slots for insertion of shield tabs. Unfortunately, having plated slots require two additional steps in the PCB manufacturing process and adds considerable cost to the resulting product.
The disadvantages associated with the prior art are overcome by an apparatus and method for shielding electrical components mounted on a printed circuit board (PCB) from electromagnetic and radio frequency interference by reducing the dissipation of heat away from the solder joints.
In an embodiment of the invention, a radio frequency (RF) shield for a printed circuit board comprises a shield for RF shielding a portion of the PCB having electronic components mounted thereon. The shield has a first portion and a second portion, wherein the first portion has a reduced cross sectional area, for reducing heat conduction between the first and the second portion when the first portion of the shield is inserted into a first plurality of apertures in the PCB, for soldering the first portion of the shield to a copper foil of the PCB.
In alternative embodiments of the invention, a plurality of apertures are disposed on the first portion of the RF shield for further reducing the heat conducted between the first and second portion. The holes are arranged linearly within the thickness of the PCB perpendicular portion.
Further embodiments of the present invention will become apparent from the detailed description contained hereinafter. It should be understood, however, that the detailed description and specific examples are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.